1. Field of the Invention
This invention relates to silver halide photographic light-sensitive materials and, more particularly, to photographic light-sensitive materials providing extremely contrasty negative image photographic characteristics.
2. Description of the Prior Art
A method of obtaining photographic characteristics of a contrasty negative image by adding a hydrazine compound to a silver halide photographic emulsion is described in U.S. Pat. No. 2,419,975. U.S. Pat. No. 2,419,975 discloses that extremely contrasty photographic characteristics, such as a gamma (.gamma.) of more than 10, can be obtained by adding a hydrazine compound to a silver chlorobromide emulsion and developing the emulsion with a developer having a pH as high as 12.8. However, strongly alkaline developers having a pH near 13 are so unstable that they tend to be oxidized by air and, therefore, cannot be used or stored for long periods of time. Moreover, development at such a high pH tends to cause fog.
Ultra-contrasty photographic characteristics, either of a negative image or of a positive image, are very useful for the photographic reproduction of an image of a continuous tone comprising a dot image which is useful in making printing plates or the reproduction of a line image. For the above purposes, hitherto a method of using a silver chlorobromide photographic emulsion having a silver chloride content of more than 50 mol%, preferably more than 75 mol%, and developing the emulsion with a hydroquinone developer having an extremely reduced effective concentration of sulfite ions (usually less than 0.1 mol/l) has been generally adopted. However, in this method, since the sulfite ion in the developer is in low concentration, the developer is very unstable and cannot withstand storage for a period exceeding 3 days. Furthermore, since a silver chlorobromide emulsion containing a relatively high percentage of silver chloride must be used, high sensitivity cannot be obtained.
Accordingly, use of an emulsion of high sensitivity and a stable developer to obtain ultra-contrasty photographic characteristics useful for the reproduction of a dot image or a line image have been strongly desired.